The problem with coil springs is they do not provide any resistance to movement so all effort is placed on the shocks. The friction as the leaf springs provide a lot of bounce dampening. Doesn't make much difference with a load that has a low COG, but with the higher COG of a truck camper, you need all the help possible to reduce sway.
To give you an example of the how much benefit, you can easily drive a leaf sprung vehicle without shocks but it is almost impossible with coil springs.
And that is just with an unloaded vehicle.
Now you could possibly get by with a coil sprung vehicle for a light weight low COG pop-up like a Palomino. But since the cost between a 3500 and 2500 is almost the same, why bother for a slightly nicer ride when running empty. Running loaded, the ride is going to be a little bed in the 3500, especially with the max load you could put in a 2500 when it sits in the 3500.
